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5.6.6 Ambisonic Equivalent (AEP)

In common with the channel based panning types we have covered so far, Ambisonics is a technology that also distributes virtual sound sources in space yet it achieves this in a fundamentally different way. Ambisonics relies on a two step process.

  1. Encoding Audio sources along with their positional information are wrapped up together using signal mathematics to create encoded Ambisonic audio. Ambisonic scenes are always carried on at least 3 channels of audio. They are not intended to be listened to directly they are intended to be decoded.
  2. Decoding Ambisonic audio signals are unwrapped and the positional information contained within them is decoded specifically for one type of speaker configuration. What we get is an immersive sound field that should accurately render the original spatial composition in 2D or 3D on the specified speaker configuration.

Keeping these two steps separate has a number of advantages. Primarily, that of being able to record the encoded Ambisonic audio signals independently of any fixed speaker arrangement. On the other hand, it is possible to “fuse” the two stages of the process together resulting in what appears to be the output of a generalised channel based type of panning. That is the ÆP panning type in a nutshell.

How does it work?

ÆP has certain computational and ambisonic mixing advantages and exhibits very different behavior from the VBAP/VBIP pairwise approaches. It is up to you to decide whether to work with purely Ambisonic rooms (more about that in the later section) or to use ÆP as a channel based panning law. Both approaches are valid and could be useful. As we have mentioned a few times already, the choice of panning type depends on what sounds best in the context of your material, your compositional goals and the acoustics of the system you are working with.